Now, a safer, more effective TB vaccine for HIV-positive people

Published: Friday, October 24, 2008, 15:52 [IST]

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Washington, Oct 24 : Scientists at University of California, Los Angeles (UCLA), have developed a new vaccine for tuberculosis (TB), which they claim is safer and more effective for HIV-positive people.

The vaccine, which has been especially designed for HIV-positive people, may help curtail the global spread of the disease, as tuberculosis has been known as a biggest cause of death in people with HIV.

"The AIDS and tuberculosis epidemics are now so intertwined in many parts of the world that we can't win the fight against one of these diseases without also taking on the other," said Dr. Marcus Horwitz, principal investigator and professor of medicine and microbiology, immunology and molecular genetics, David Geffen School of Medicine at UCLA.

The current vaccine against tuberculosis, called BCG, can cause serious and even fatal disease in HIV-positive people later in life, if HIV weakens the immune system, allowing the vaccine to multiply unchecked and spread throughout the body.

Aiming to solve this problem, the researchers used an innovative method to limit the number of times the new vaccine can replicate in the body -- just enough to stimulate the immune system to produce T cells to fight future infection with the tuberculosis bacillus, but not enough to overwhelm the immune system if it subsequently becomes weakened by HIV.

The researchers showed that the new vaccine better protects guinea pigs from tuberculosis than the current vaccine. They also showed that the new vaccine is much safer than BCG in a severely immunocompromised animal host - mice with Severe Combined Immunodeficiency (SCID mice) that completely lack an immune system.

The new vaccine was specifically designed to be given to HIV-positive newborns and adults whose immune systems haven't been affected much are thus capable of mounting a good immune response to the vaccine, including persons on antiretroviral therapy.

For developing the new vaccine, the scientists modified the current BCG vaccine, which is a weakened form of a bacterium closely related to the one that causes tuberculosis.

Thus, the researchers first made so that it would produce large amounts of a key protein of Mycobacterium tuberculosis, called mycolyl transferase, hence making the vaccine more potent and induce a stronger immune response.

Them, in order to make it safer, the team altered the BCG vaccine so that it was only capable of multiplying a few times after it was injected into the body. They, thus, eliminated the vaccine's ability to acquire iron from the host; iron is an essential nutrient for the vaccine to multiply.

It is believed that since iron is a key nutrient needed by all bacteria to thrive, this approach may be applicable to other live bacterial vaccines for diseases such as anthrax, tularemia and Legionnaires' disease.

Now, the researchers are hoping to test the vaccine in humans.

The study is published in the latest edition of the journal Infection and Immunity.